Basic Concepts in BiomechanicsBasic Concepts in BiomechanicsLecture 1Lecture 1

AC1101AC1101Dr. J. Kim RossDr. J. Kim Ross

DefinitionDefinition

Biomechanics is the study of mechanics in the Biomechanics is the study of mechanics in the human body.human body.

Why are we interested in biomechanics as Why are we interested in biomechanics as chiropractors?chiropractors?

Because spinal manipulation is Because spinal manipulation is a biomechanical intervention!a biomechanical intervention!

Subdivisions of BiomechanicsSubdivisions of Biomechanics

Biomechanics

KineticsKinematics

KinematicsKinematics

The division of biomechanics that describes The division of biomechanics that describes motion without consideration of the forces motion without consideration of the forces that cause the motion.that cause the motion.

KineticsKinetics

The division of biomechanics that is The division of biomechanics that is concerned with the forces producing motion concerned with the forces producing motion or maintaining equilibriumor maintaining equilibrium

KinematicsKinematics

The kinematic variables include:The kinematic variables include: 1) Types of Motion1) Types of Motion 2) Location of Motion2) Location of Motion 3) Direction of Motion3) Direction of Motion 4) Quantity of Motion4) Quantity of Motion

1) Types of Motion1) Types of Motion

A) Rotatory (Angular) MotionA) Rotatory (Angular) Motion B) Translatory (Linear) MotionB) Translatory (Linear) Motion C) Curvilinear MotionC) Curvilinear Motion D) General Plane MotionD) General Plane Motion

A) Rotatory (Angular) MotionA) Rotatory (Angular) Motion

Movement of a segment around a fixed axis Movement of a segment around a fixed axis in a curved path.in a curved path.

Each point on the segment moves through Each point on the segment moves through the same angle at the same time at a the same angle at the same time at a constant distance from the axis of rotationconstant distance from the axis of rotation

Few joints if any move around a truly fixed Few joints if any move around a truly fixed axisaxis

However they are often described as though However they are often described as though they do.they do.

Figure 1. Angular Motion. When this arm moved from horizontal (white) to a 45 degree angle (red), all points on that arm moved through the same angle but clearly point B traveled a greater distance.

AA

B

B

A

A) Rotatory (Angular) MotionA) Rotatory (Angular) Motion

B) Translatory (Linear) MotionB) Translatory (Linear) Motion

Movement of a segment in a straight line.Movement of a segment in a straight line. Each point moves through the same Each point moves through the same

distance at the same time in parallel paths.distance at the same time in parallel paths. Occurs when one bone is pulled away from Occurs when one bone is pulled away from

or pushed toward it’s joint.or pushed toward it’s joint. When one flat contiguous joint surface When one flat contiguous joint surface

translates along another, this is also translates along another, this is also translatory motion and is referred to as translatory motion and is referred to as glidinggliding. .

B) Translatory (Linear) MotionB) Translatory (Linear) Motion

Eg of translatory motion external to a joint is Eg of translatory motion external to a joint is forward movement of the hand and forearm.forward movement of the hand and forearm.

The movement is actually produced by The movement is actually produced by rotation at both the elbow and shoulder rotation at both the elbow and shoulder joints.joints.

A

C

B

C

B

A

Figure 2. Linear Motion. When this box was moved from left to right each point on the box moved the same distance (note that the three arrows are the same length.

B) Translatory (Linear) MotionB) Translatory (Linear) Motion

C) Curvilinear MotionC) Curvilinear Motion

Rotatory and translatory motion combined.Rotatory and translatory motion combined. Rotation around a joint is accompanied by Rotation around a joint is accompanied by

gliding of the articular surfaces.gliding of the articular surfaces. This produces a moving axis and therefore This produces a moving axis and therefore

curvilinear action.curvilinear action. This is the most common form of motion This is the most common form of motion

produced at a joint.produced at a joint. Gliding is slight and hence motion described Gliding is slight and hence motion described

as though it was pure rotation.as though it was pure rotation.

D) General Plane MotionD) General Plane Motion

Object rotates about an axis while the axis is Object rotates about an axis while the axis is translated in space by motion of another translated in space by motion of another segment.segment.

Forearm rotates around the elbow as the Forearm rotates around the elbow as the elbow joint is translated by the upper arm.elbow joint is translated by the upper arm.

2) Location of Motion2) Location of Motion

A) Transverse PlaneA) Transverse Plane B) Frontal (Coronal) B) Frontal (Coronal)

PlanePlane C) Sagittal PlaneC) Sagittal Plane Frontal Plane

Sagittal Plane

Transverse Plane

Figure 3. The planes of motion.

A) Transverse PlaneA) Transverse Plane

Divides the body into upper and lower Divides the body into upper and lower halveshalves

Movement in this plane occurs parallel to Movement in this plane occurs parallel to the ground.the ground.

Eg. Movement of the nose when rotating the Eg. Movement of the nose when rotating the head.head.

B) Frontal (Coronal) PlaneB) Frontal (Coronal) Plane

Divides the body into front and back halves.Divides the body into front and back halves. Eg. Bringing the ear to both shoulders Eg. Bringing the ear to both shoulders

requires the head to move through a frontal requires the head to move through a frontal plane.plane.

C) Sagittal PlaneC) Sagittal Plane

Divides the body into left and right halves.Divides the body into left and right halves. Eg. Nodding the head as if to indicate yes Eg. Nodding the head as if to indicate yes

requires sagittal plane motion.requires sagittal plane motion.

3) Direction of Motion3) Direction of Motion

A) FlexionA) Flexion B) ExtensionB) Extension C) AbductionC) Abduction D) AdductionD) Adduction E) Medial (Internal) RotationE) Medial (Internal) Rotation F) Lateral (External) RotationF) Lateral (External) Rotation G) CompressionG) Compression H) DistractionH) Distraction

A) FlexionA) Flexion

Refers to rotation of a body segment around Refers to rotation of a body segment around a joint axis so that the ventral surfaces are a joint axis so that the ventral surfaces are being approximated.being approximated.

Exception is the Knee and Foot Exception is the Knee and Foot During development the surfaces rotate 180 During development the surfaces rotate 180

degreesdegrees Sagittal plane motionSagittal plane motion

B) ExtensionB) Extension

Refers to rotation of a body segment around Refers to rotation of a body segment around a joint axis so that the dorsal surfaces are a joint axis so that the dorsal surfaces are being approximated.being approximated.

Sagittal plane motionSagittal plane motion

C) AbductionC) Abduction

Rotation of a segment around an axis so Rotation of a segment around an axis so that the distal segment moves that the distal segment moves awayaway fromfrom the midline of the body.the midline of the body.

Occurs in the frontal planeOccurs in the frontal plane

D) AdductionD) Adduction

Rotation of a segment around an axis so Rotation of a segment around an axis so that the distal segment moves that the distal segment moves towardstowards the the midline of the body.midline of the body.

Occurs in the frontal planeOccurs in the frontal plane

E) Medial (Internal) RotationE) Medial (Internal) Rotation

Motion in the transverse plane around a Motion in the transverse plane around a longitudinal axis longitudinal axis towardtoward the midline of the the midline of the body.body.

If the segment is part of the midline of the If the segment is part of the midline of the body (ie. the spine) then the rotation is body (ie. the spine) then the rotation is simply termed left or right rotation. The simply termed left or right rotation. The designation is with respect to the anterior designation is with respect to the anterior portion of the body.portion of the body.

F) Lateral (External Rotation)F) Lateral (External Rotation)

Motion in the transverse plane around a Motion in the transverse plane around a longitudinal axis longitudinal axis away fromaway from the midline of the midline of the body.the body.

G) CompressionG) Compression

Translatory motion of a segment Translatory motion of a segment towardtoward it’s it’s joint.joint.

H) DistractionH) Distraction

Translatory motion of a segment Translatory motion of a segment away fromaway from it’s joint.it’s joint.

4) Quantity of Motion4) Quantity of Motion

A) RotatoryA) Rotatory– Measured in degrees or radiansMeasured in degrees or radians

B) TranslatoryB) Translatory– Measured in inches or centimetres etc.Measured in inches or centimetres etc.